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Tuesday, 31 March 2015

The Reason You Have An Apple-Shaped (Or Pear-Shaped) Body

If you’ve ever read a women’s magazine, you’re familiar with the concept of “apple” versus “pear” body shapes. They’re the two most common presentations of the human body — in the first case, fat gathers around the midsection, in the latter, fat accumulates around the hips, thighs, and rear.

Now, researchers from Duke University have pinpointed a gene, called Plexin D1, which determines the body type you’ll have with a great deal more certainty than any magazine quiz ever could.

Now, for those who think that your body shape is only a barometer of the style of jeans you choose, or if you should opt for the A-line vs. the empire waist wedding dress, take heed: Your body shape has everything to do with your health.

An apple shaped body, which has greater fat accumulation in the belly, carries with it the risk of heart disease. Fat concentration in the midsection is also thought to induce inflammation and trigger metabolic diseases including high blood pressure, stroke and diabetes.

A pear body shape, on the other hand, is considered to be pretty healthy. This shape accumulates fat in the hips and thighs, which is associated with increased fertility and a decreased risk of metabolic diseases like diabetes.

Now let’s get back to that study.

All humans have the Plexin D1 gene. But to simplify their research, the Duke researchers chose to study the gene’s effects in zebrafish. Since the fish are transparent, you can actually see where the fat cells are accumulating to easily determine their body shape. John F. Rawls, PhD, and an associate professor of molecular genetics and microbiology at Duke, and James E. Minchin, PhD, a post-doctoral fellow in Rawls’ lab, engineered zebrafish without the Plexin D1 gene, and compared them with normal zebrafish who carried the gene.

The fish without the Plexin D1 gene had less visceral fat tissue than their “apple-shaped” counterparts with the gene. Visceral fat is the type of fat that causes an apple-shaped body. It lies deep within the midsection, wedged between organs including the heart, liver, intestine, and lungs. From there, the tissue emits hormones and other chemicals that cause inflammation, triggering high blood pressure, heart attack, stroke, and diabetes.

Instead, these “pear shaped” fish displayed more subcutaneous fat, which is the type of fat that sits beneath the skin of the hips, thighs, and rear of pear-shaped individuals. This type of fat tissue decreases insulin resistance in humans — which protects us from getting diabetes.

So should we all try to get rid of our Plexin D1 gene? Not so fast. Michin tells Yahoo Health, that while “to have such an extreme effect is surprising,” it’s important to remember that their research also involved an extreme amount of genetic manipulation, wholly eliminating the Plexin D1 gene in the mutant zebrafish in a way that is unlikely to ever occur in real life.

All humans carry the Plexin D1 gene, but we express the gene in different ways. “Body fat distribution is a complex trait that is governed by interactions between multiple genes, says Michin. “We expect that more subtle regulation of Plexin D1 in human populations is likely to occur.”

Despite the clear health implications of body fat distribution, little is known about the genetics of body shape. A large international study that appeared in Nature in February began to fill in this gap by looking for genes associated with waist-to-hip ratio. The researchers found some association with Plexin D1 in their study. read here

In the future, this information could lead to understanding how to genetically manipulate our body types — and, more importantly, improve our health in the process.